Table of Content

15 June 2019, Volume 30 Issue 6

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Special Features of Stable Isotope Ecology

Ecohydrologic separation of the mixing process between precipitation and soil water: A review.

LYU Si-dan, SONG Xian-wei, WEN Xue-fa

2019, 30(6):  1797-1806.  doi:10.13287/j.1001-9332.201906.010

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Within the framework of traditional translatory flow, infiltrating precipitation and water at any soil depth is firstly well mixed and eventually enters the stream. Based on the dual stable isotope approach (δD and δ¹⁸O), recent studies showed that ecohydrologic separation occurs during the mixing process between precipitation and soil water. Namely, soil water has two pools: soil bound water which includes unavailable and available water used by plants, and soil mobile water entering the stream. The partial mixing of both water pools is defined as hydrologic connectivity. In this review, the concept and meaning of ecohydrologic separation are explained systematically. We described the mixing process between precipitation and soil water, and water isotopes (δD and δ¹⁸O) of soil bound water and mobile water in detail. We summarized the advantages and disadvantages of the direct and substitute methods to measure δD and δ¹⁸O in soil water, bound water, and mobile water. We reviewed the researches on hydrologic separation and connectivity of soil bound water and mobile water in runoff plot and watershed, including the qualitative research based on the direct and substitute methods, and the quantitative research using the models and control experiments. At last, we proposed that further studies should strengthen the research on the qualitative and quantitative methods of ecohydrological separation, and their influences on traditional ecohydrology models.

Stable isotopes of zooplankton and their applications in the research of aquatic ecosystems

HOU Wei, SUN Shao-hua, GU Bin-he, SUN Li, HU Fang, WANG Ming-quan, ZHAO Qing-hua, JIA Rui-bao

2019, 30(6):  1807-1814.  doi:10.13287/j.1001-9332.201906.016

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Zooplankton plays a mediating role in the food web of aquatic ecosystems, the stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) of which have been widely used to study the utilization of food resources, material cycling pathways, and trophic relationships. The δ¹³C and δ¹⁵N values of zooplankton have been used to predict primary productivity, sources and sinks of pollutants and environmental changes. To better use δ¹³C and δ¹⁵N of zooplankton as ecological and environmental indicators, it is particularly important to understand their temporal and spatial variations and the influencing factors. Based on related literature, we synthesized spatial and temporal variations in δ¹³C and δ¹⁵N of zooplankton in different aquatic ecosystems and taxa groups, and the use of δ¹³C and δ¹⁵N indicators for ecological processes and environmental changes. The δ¹³C and δ¹⁵N of zooplankton are largely affected by its food sources, and its stable isotope compositions are in turn affected by primary productivity and nitrogen sources. We proposed that the combination of δ¹³C and δ¹⁵N in zooplankton with transportation and transformation of emerging pollutants would form a multi-means, multi-disciplinary and multi-scale research direction in the fields of earth science and biology.

Geographical variation and the response to hydrothermal factor of stable carbon isotope (δ¹³C) in Pinus massoniana.

ZHANG Zhen, JIN Guo-qing, ZHOU Zhi-chun, FENG Zhong-ping, SUN Lin-shan

2019, 30(6):  1815-1822.  doi:10.13287/j.1001-9332.201906.007

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We used 10 representative provenances at different latitudes in two 33-year-old Pinus massoniana provenance test stands (Chun’an Laoshan in Zhejiang and Taizi Mountain Shilong in Hubei) to measure the differences among provenances, study the geographical variation, and identify its responses to hydrothermal factors. The results showed that the δ¹³C of the average annual rings was significantly different among the provenances of P. massoniana, being higher in trees from high latitude than from low latitude. The δ¹³C of average annual rings showed a zonal variation trend, indicating an adaptation to the original environment. The δ¹³C of annual rings was negatively correlated with mean annual temperature (MAT), mean temperature in January (T₁), annual precipitation (MAP), precipitation from May to September (P_5-9) and cumulative temperature above 10 ℃ (CT). It was positively correlated with the aridity index (AI). The response function of AI toδδ¹³C annual rings in Chun’an and Taizi Mountain explained 37.5% and 42.5% of the variation, respectively, indicating that AI was the most important limiting factor. The Taizi Mountain test site in Hubei Province located in the central and western region with relatively dry soil and high aridity. Therefore, the δ¹³C of the average annual ring was 1.8% higher than that in the Chun’an test site. The δ¹³C rings of P. massoniana at the Taizi Mountain and Chun’an were sensitive to the temperature in July and August, respectively. Summer precipitation was the main factor for carbon isotope fractionation with stable rings. The sensitivity of different provenances to future climate changes was different.

Characteristics of hydrogen and oxygen isotopes in precipitation and moisture sources in Gaoyou, Jiangsu Province, China

SUI Ming-zhen, GAO De-qiang, XU Qing, HE Dong-mei, WANG Lei, WANG Ting

2019, 30(6):  1823-1832.  doi:10.13287/j.1001-9332.201906.009

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It is necessary to examine the characteristics of hydrological cycle in Gaoyou area of Jiang-su Province in response to climate change and flood disasters. In this study, 121 atmospheric rain samples were collected and environmental factors were recorded from July 2015 to October 2017. We analyzed the hydrogen and oxygen stable isotopic composition of rain and identify moisture sources in this area. Results showed that the hydrogen and oxygen isotopic composition of rain had an seasonal variation, which was positive in the winter but negative in the summer. D-excess value was higher in winter than that in summer. On the annual scale, significantly negative relationships between δD (δ¹⁸O) and temperature and between δD (δ¹⁸O) and precipitation indicated the “anti-temperature effect” and “precipitation amount effect”, respectively. On the seasonal scale, there was no obvious “temperature effect” but “precipitation amount effect” in autumn and winter. Results from the HYSPLIT model showed that the precipitation in this area came mainly from ocean evaporation that was influenced by the Chinese South Sea, Indian Ocean and Pacific Ocean. Precipi-tation in other seasons mainly came from the water vapor mixture from the Eurasian continent, Atlantic Ocean, Arctic Ocean, as well as local evaporation. The seasonal pattern of δD and δ¹⁸O values in precipitation was mainly influenced by monsoon activity and El Niño-Southern Oscillation (ENSO). In addition, the precipitation isotopes clearly indicated the shift in climates from El Niño to La Niña.

Foliar stable carbon isotope composition and water use efficiency of plant in the Karst seasonal rain forest.

HUANG Fu-zhao, LI Dong-xing, WANG Bin, XIANG Wu-sheng, GUO Yi-li, WEN Shu-jun, CHEN Ting, LI Xian-kun

2019, 30(6):  1833-1839.  doi:10.13287/j.1001-9332.201906.008

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To enrich niche partition and species coexistence theory in karst seasonal rain forest, and provide reference for species selection and configuration for rocky desertification control, we exami-ned foliar stable carbon isotope composition (δ¹³C) and water use efficiency (WUE) of the representative species in different habitats and the same tree species in different habitats. The results showed that foliar δ¹³C value in karst seasonal rain forest ranged from -34.13‰ to -29.69‰, with a mean value of (-31.40±1.19)‰. WUE ranged from 9.08-58.76 μmol·mol^-1, with a mean value of 41.79 μmol·mol^-1. Both of them were lower than subtropical and warm temperate forests at higher latitude, but higher than tropical rain forests at lower latitude and non-karst seasonal rain forests at the same latitude. The foliar δ¹³C value and WUE of representative species gradually increased with the increases of drought index from the depression to the top of the mountain. The foliar δ¹³C value and WUE of the same tree species increased with altitude. These results indicated that water use efficiency of tree species was not only related to climate factors, but also related to the geological background and water availability of the habitat. The water use efficiency of plants in karst area was higher than that in non-karst area, and was higher in dry habitat than in wet habitat under the same climatic condition. It showed that having different water use efficiencies was one of the strategies for plants in karst area to adapt to different habitats and maintain species coexistence.

Effects of extraction methods on soil water isotope and plant water source segmentation.

MA Xiao-jun, JIN Jing-jing, SI Bing-cheng, XIANG Wei, WANG Hong-xiu

2019, 30(6):  1840-1846.  doi:10.13287/j.1001-9332.201906.013

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We used two types of soil with different physicochemical properties (loam and sand), oven-dried them, and then added the known isotopic composition mineral water that was reference water to compose the soil-water mixture with different soil water contents (loam: 0.15, 0.20, 0.30 g·g^-1; sand: 0.10 g·g^-1). After that, we set up different equilibrium time (loam: 3, 6, 12, 24, 48, 72, 96 h; sand: 96 h) to ensure that the dry soil particles were well mixed with the added water. The soil water was extracted by mechanical centrifugation and cryogenic vacuum extraction after equilibrium, and their isotope composition was analyzed. Results showed that the isotopic values of soil water extracted by mechanical centrifugation method had no significant difference in same water content with different equilibration times, but were more enriched compared with the reference water isotopic value. The maximum enrichment for hydrogen and oxygen isotope was 7.38‰ and 1.24‰, respectively. In contrast, cryogenic vacuum extraction method resulted in more depleted soil water isotopes than reference water, with the maximum depletion for hydrogen and oxygen isotope being 6.27‰ and 1.03‰, respectively. Moreover, the degree of depletion increased with the increases of equilibrium time (less than 24 h) at low water content, and became stable after 24 h. With the increases of soil water content, the isotopic composition of the extracted soil water was less affected by the two extraction methods. The water isotope value of loam that had high clay content, was more sensitive to the extraction method than the sandy soil that had low clay content. The difference of isotopic composition caused by extraction methods did not affect the plant water source segmentation.

Hypobromite oxidation combined with hydroxylamine hydrochloride reduction method for analyzing ammonium nitrogen isotope in atmospheric samples.

XIANG Yan-kun, CAO Fang, YANG Xiao-ying, ZHAI Xiao-yao, ZHANG Yan-lin

2019, 30(6):  1847-1853.  doi:10.13287/j.1001-9332.201906.011

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Ammonium salts, including ammonium nitrate, ammonium sulfate and ammonium hydrogen sulfate, are the main components of secondary inorganic aerosols and play an important role in the formation of haze events. The sources and transformation processes of atmospheric ammonium have received more and more attention. In this study, we modified the previous stable isotope analysis technique by improving the injection volume and adding a pH adjustment step, which gave a rapid and accurate measurement of ammonium nitrogen isotope ratio in atmospheric aerosol samples. Firstly, we added alkaline hypobromite to the extracted solution of the atmospheric aerosol filter samples (0.25 μg·mL^-1 ammonium nitrogen in 4 mL) to oxidize ammonium (NH₄⁺) to nitrite (NO₂^-). Then, after adjusting the pH, nitrite (NO₂^-) was reduced to nitrous oxide (N₂O) by hydroxylamine hydrochloride under pH <0.3. Finally, nitrous oxide (N₂O) was analyzed by Precon-GasBench-IRMS system to measure ammonium nitrogen isotope ratio. Our approach required low amount of NH₄⁺ and avoided the use of highly toxic and explosive reagents. Meanwhile, the precision of our method could reach as high as 0.2‰ (n=10). This method could increase the NH₄⁺ reduction efficiency to 100% at a condition of pH <0.3 and satisfy the demands of precision and accuracy for determination of ammonium nitrogen isotope in atmospheric aerosol samples. This method would help us better understand the sources, evolutions, chemical and deposition processes of atmospheric ammonium.

Effects of exogenous ABA on translocation of photosynthate to fruit of Fuji apple during late stage of fruit rapid-swelling.

SHA Jian-chuan, JIA Zhi-hang, ZHANG Xin, WU Xiao-xian, GE Shun-feng, JIANG Yuan-mao

2019, 30(6):  1854-1860.  doi:10.13287/j.1001-9332.201906.017

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To clarify the effects and underlying mechanism of ABA on sugar accumulation in apple fruits, ¹³C trace technique was used to examined the effects of different ABA levels (0, 50, 100 and 150 mg·L^-1) and fluoridone (ABA biosynthesis inhibitor) on translocation of photosynthate to fruit during late stage of fruit rapid-swelling in five-year-old ‘Yanfu3’/M26/Malus hupehensis Rehd. The results showed that the activities of related enzyme in sugar metabolism, the relative expression of sucrose transporter gene MdSUT1, MdSUT2.2 and sorbitol transporter gene MdSOT3 tended to increase first and then decrease with increasing ABA concentration, with a peak in 100 mg·L^-1ABA treatment. Fluridone treatment significantly inhibited the enzymes activities of sugar metabolism and the relative expression of sugar transporters. The treatment of 100 mg·L^-1ABA significantly reduced leaf ¹³C content, increased fruit ¹³C content and increased the transport rate of photosynthate from leaves to fruits compared with other treatments. Our results indicated that exogenous ABA enhanced sink strength of fruit and promoted the transportation of more photosynthate to fruits, which increased the soluble sugar content in fruits.

Effects of potassium supply on the growth, photosynthesis and ¹⁵N and ¹³C absorption and utilization of M9T337 seedling.

XU Xin-xiang, HOU Xin, JIA Zhi-hang, YU Tian-wu, GE Shun-feng, JIANG Yuan-mao

2019, 30(6):  1861-1868.  doi:10.13287/j.1001-9332.201906.012

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Hydroponic experiment was carried out on M9T337 seedlings using ¹⁵N and ¹³C isotope tracer technology to study the effects of different potassium supply levels (K₀, K₁, K₂, K₃ and K₄ were equivalent to 0, 3, 6, 9 and 12 mmol·L^-1, respectively) on the growth, photosynthetic characteristics and ¹⁵N and ¹³C absorption and utilization of M9T337 seedlings. The results showed that dry mass, root length, root surface area, number of tips and root activity of M9T337 seedlings under the K₂ level were significantly higher than those under other levels. The net photosynthetic rate (P_n) of leaves increased at low K⁺ concentration and then decreased with the increases of potassium supply level, and reached the maximum value at K₂ treatment (15.5 μmol CO₂·m^-2·s^-1). At the 30th day after treatment, the activities of nitrate reductase (NR) and carbon metabolism enzyme were highest in K₂ treatment, and lowest in K₀ treatment. With the increases of potassium application rate, the ¹³C accumulation of seedlings were first increased and then decreased, with the ¹³C distribution rate of each organ being the most balanced at K₂ treatment. There were significant differences in ¹⁵N uptake and utilization rate among treatments. ¹⁵N uptake and utilization rates of seedlings under K₂ treatment were the highest, which were 16.1 mg and 17.9%, respectively. Therefore, too low or too high potassium supply could inhibit seedling root growth and leaf photosynthesis, which was not conducive to carbon and nitrogen absorption. Appropriate potassium supply could improve root activity and net photosynthetic rate, enhance nitrate reductase (NR) and carbon metabolic enzyme activity, and promote carbon and nitrogen metabolism.

Effects of organic fertilizer application on accumulation and distribution of assimilates in winter wheat

ZHANG Dai-jing, CHEN Qian-qing, ZONG Jie-jing, YANG Xue-qian, HU Xiao, MA Jian-hui

2019, 30(6):  1869-1876.  doi:10.13287/j.1001-9332.201906.014

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To understand the effects of organic fertilizer addition on accumulation and distribution of winter wheat assimilates, we compared organic carbon content in soil and wheat plants, photosynthetic characteristics and assimilation transformation under two different fertilizer treatments, CF (chemical fertilizer only) and OF (organic fertilizer with chemical fertilizer), using ¹³CO₂ pulse labeling method. The results showed that OF increased soil organic carbon content and wheat photosynthetic parameters, resulting in higher organic carbon content and total dry biomass accumulation in wheat plants compared with CF treatment. Compared marking to maturity with that on the 7th day after the same marking, the content and distribution rate of ¹³C in leaves and stems of two treatments decreased; the ¹³C content in spikes increased at jointing stage and filling stage, decreased at anthesis stage, and the ¹³C distribution rate increased at all stages. OF treatment was more beneficial for the transportation of photosynthetic product from leaves to spikes at filling stage, with higher ¹³C distribution rate in spikes compared with CF treatment. The results of correlation analysis showed that dry matter accumulation was significantly positively correlated with the net input of ¹³C content and its distribution rate, but negatively correlated with organic carbon content in plants. The net input of ¹³C content was significantly positively correlated with its distribution rate, and negatively correlated with F_v/F_m and P_n. In conclusion, organic fertilizer application could increase the content of organic carbon in soil, improve wheat plants photosynthetic capacity and transportation of photosynthetic product to spikes, and ultimately increase dry matter accumulation in wheat spikes.

Soil organic carbon mineralization and priming effects in the topsoil and subsoil under no-tillage black soil.

HUANG Shuang-shuang, HUO Chang-fu, XIE Hong-tu, WANG Peng, CHENG Wei-xin

2019, 30(6):  1877-1884.  doi:10.13287/j.1001-9332.201906.015

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Priming effect is one of the important mechanisms regulating soil organic matter decomposition. However, the variation of priming effects in different soil layers remains unclear. In this study, we conducted a 30-day incubation experiment using no-tillage black soil from northeastern China. ¹³C-glucose and dynamic CO₂ trapping methods were employed to investigate soil organic carbon (SOC) mineralization rates and the priming effect of the added ¹³C-glucose in the upper soil layer (0-10 cm) and the lower soil layer (30-40 cm). Our results showed that the cumulative SOC-specific mineralization rate in the upper layer was similar to that in the lower layer soil without glucose addition. Glucose addition significantly altered the mineralization rates in both layers, resulting in a positive priming effect (36.7%) in the upper layer but a negative priming effect (-12.4%) in the lower layer. The cumulative priming effect during the 30-day incubation was 3.24 mg C·g^-1 SOC for the upper layer soil and -1.24 mg C·g^-1 SOC for the lower layer soil. There was still a net SOC increase, even with positive priming effects in the upper layer soil. This was due to considerable amount of added glucose-C remained un-mineralized in the soil which would compensate the carbon loss from priming effects. Overall, our results demonstrated that the magnitude and direction of priming effects might differ between soil layers. Our findings contribute to a better understanding of the effects of conservation tillage practices (no-tillage and straw incorporation) on soil organic matter dynamics in agroecosystems.

Original Articles

Spatial variation of carbon density in Pinus massoniana forest in Jiangxi Province, China

PAN Ping, SUN Yu-jun, OUYANG Xun-zhi, RAO Jin-feng, FENG Rui-qi, YANG Zi-yun

2019, 30(6):  1885-1892.  doi:10.13287/j.1001-9332.201906.040

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Carbon density is one of the important indicators for carbon sequestration capacity in forest ecosystems. The analysis of spatial variation in forest carbon density can provide scientific basis for management of forest carbon sink. We investigated the carbon density of Pinus massoniana forest in Jiangxi Province. Based on plot investigation and meaurement of sample carbon content, the spatial autocorrelation and distribution of carbon density were analyzed and explored respectively by using global Moran I, local Moran I and geostatistics. Results from the global Moran I showed that ecosystem carbon density had significant positive spatial autocorrelation and its autocorrelation decreased with the increase of distance. Ecosystem carbon density had no spatial autocorrelation when the distance exceeded 400 km. The spatial distribution of ecosystem carbon density changed from aggregated distribution to random distribution with the increase of distance. Results from the local Moran I showed that the local spatial distribution of ecosystem carbon density was not uniform, and the difference of local spatial distribution gradually increased with the increase of distance. The fitting results of semi-variogram models showed that the spherical model was the best fitting model for the estimation of ecosystem carbon density. The ratio of nugget to sill was 0.36, indicating mode-rate spatial correlation of carbon density. The ecosystem carbon density based on kriging spatial interpolation mainly concentrated in the range of 85.14-153.52 t·hm^-2. The spatial distribution regularity was generally low in middle region and high in peripheral region, which was consistent with the terrain characteristics of the study area.

Effects of warming on microbial biomass carbon and nitrogen in the rhizosphere and bulk soil in an alpine scrub ecosystem

MA Zhi-liang, ZHAO Wen-qiang, LIU Mei, LIU Qing

2019, 30(6):  1893-1900.  doi:10.13287/j.1001-9332.201906.024

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To understand the effects of climate warming on the rhizosphere ecological process in the alpine scrub ecosystem, the responses of microbial biomass carbon and nitrogen in the rhizosphere and bulk soil to experimental warming were examined in a Sibiraea angustata scrubland on the eas-tern Qinghai-Tibetan Plateau, China. The results showed that the concentrations of microbial biomass carbon and nitrogen in the rhizosphere and bulk soil in the early growing season were significantly higher than those in the middle and late growing seasons. Experimental warming did not significantly affect the concentrations of microbial biomass carbon and nitrogen of the rhizosphere soil in the most growing seasons. In the bulk soil, however, the effects of experimental warming on the microbial biomass carbon and nitrogen differed among the growing season. Experimental warming significantly decreased microbial biomass carbon but increased microbial biomass nitrogen in the early growing season. In the middle growing season, warming significantly increased both microbial biomass carbon and nitrogen. In the late growing season, there was no significant effect. The rhizosphere effects of soil microbial biomass carbon and nitrogen also differed with the growing season. The rhizosphere effects of microbial biomass carbon and nitrogen were negative in the early growing season but positive in the middle growing season. In the late growing season, there were negative rhizosphere effects of soil microbial biomass carbon and positive rhizosphere effects of soil microbial biomass nitrogen. Furthermore, experimental warming significantly increased the rhizosphere effects of soil microbial biomass carbon and nitrogen in the early growing season, but decreased those in the middle and late growing seasons. These results uncovered the changing mechanism of the biologi-cal process in the rhizosphere and bulk soil in the alpine scrub ecosystems under the background of climate warming.

Characteristics of soil microbial biomass carbon and nitrogen and its seasonal dynamics in four mid-subtropical forests

LIU Bao, WU Wen-feng, LIN Si-zu, LIN Kai-min

2019, 30(6):  1901-1910.  doi:10.13287/j.1001-9332.201906.028

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Taking evergreen broad-leaved forest in mid-subtropical areas, and its converted Phoebe bournei, Phyllostachys heterocycla and Cunninghamia lanceolata plantations as research objects, microbial biomass carbon (MBC) and nitrogen (MBN) in the surface (0-10 cm) and deep soil layer (40-60 cm) were measured by chloroform fumigation and extraction method, with their seasonal dynamics and the relationships with soil physicochemical properties in four types of forests being investigated. The results showed that the MBC and MBN in the surface soil was the highest in the evergreen broad-leaved forest, followed by P. bournei, P. heterocycla and C. lanceolata plantations, with that in the former three being significantly higher than in C. lanceolata plantion. There was no significant difference in the MBC and MBN contents in the deep soil layer among the four types of forests, while those in surface soil were significantly higher than in the deep soil layer. The MBC and MBN contents showed obvious seasonal dynamics, with highest values in summer and lowest in winter presenting a single peak change pattern. MBC and MBN had significantly positive correlations with soil total carbon (TC), total nitrogen (TN) and temperature, but significantly negative correlation with soil bulk density. The conversion of evergreen broad-leaved forest to the three plantation resulted in lower MBC and MBN in the surface soil to some degree, with C. lanceolata plantation being the first to be affected, but little change occurred in the deep soil layer. The quantity and quality of litter, contents of TC, TN and soil temperature were the key factors driving the differences of MBC and MBN contents and their seasonal dynamics of the four types of forests.

Variations in topsoil carbon and nitrogen contents of five temperate plantations in Northeast China.

WANG Xin-qi, WANG Chuan-kuan

2019, 30(6):  1911-1918.  doi:10.13287/j.1001-9332.201906.003

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Afforestation is an effective way for carbon (C) sequestration, which also profoundly influences soil nitrogen (N) dynamics in the forest ecosystem. The impacts of tree species on soil C and N budgets and the underlying mechanism remain uncertain. In this study, we used a common garden experiment and measured the soil organic C (C_soil) and total N contents (N_soil) of the topsoil (0-10 cm) and related vegetative and soil microbial properties in 2007 and 2015 (3 and 11 years after afforestation), respectively. Our aim was to explore the effects of five major tree species (i.e., Fraxinus mandshurica, Juglans mandshurica, Betula platyphylla, Larix gmelinii and Pinus sylvestris var. mongolica) in the temperate forests in Northeast China on soil C and N contents and their dri-vers. The results showed that both C_soil and N_soil of the five stands decreased as the stand ages increased, the change rates of which were significantly correlated with each other. The rate of change in C_soil(2.6%·a^-1-4.8%·a^-1) was significantly greater than that in N_soil(0.8%·a^-1-2.8%·a^-1). The decrements of the C_soil and N_soil for the broadleaved stands were significantly lower than those of the coniferous stands. The tree-species traits and microbial properties together explained 68.5% and 90.9% of the variability of the change rates of C_soil and N_soil, respectively. The change rates of C_soil and N_soil decreased with the increases in leaf litter C/N and microbial biomass C/N, but increased with the increases of fine root biomass, microbial biomass C, and the ratio of the C-acquisition to the N-acquisition enzyme activity. Additionally, the change rate of N_soil decreased with the increases of the leaf litter production and the microbial metabolic activity. Our findings indicated that C and N contents in the topsoil of these temperate plantations decreased significantly 11 years after afforestation, while the different change rates mainly resulted from different properties of tree species and soil microbes.

Moderate grazing increases the abundance of soil methane-oxidizing bacteria and CH₄ uptake rate in a typical steppe of Inner Mongolia, China.

ZHANG Jun-zhen, ZHOU Di, GUO Xu-dong, GUO Ying, WANG Hao, CHENG Jian-wei, BAO Zhi-hua, BAOYIN Taogetao, LI Yong-hong

2019, 30(6):  1919-1926.  doi:10.13287/j.1001-9332.201906.035

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Microbial oxidation is the only biological sink of atmospheric methane (CH₄). It is essential to understand the variation of CH₄ fluxes among different grassland use types for developing low-emission management system. Here, we measured the CH₄ flux and the soil methane-oxidizing bacteria abundance in a typical steppe under grazing, mowing and fencing management in central Inner Mongolia, with the aims to determine the effects of these grassland use types on CH₄ flux, and to test the hypothesis that pmoA functional gene abundance regulates CH₄ fluxes. The measurements were conducted on the experimental grassland that had experienced four grassland use treatments over five years. The treatments were whole growing season grazing from May to September (T₁), spring and summer grazing (twice in May and July)(T₂), autumn mowing (T₃) and enclosure (T₀). We measured CH₄ flux using static chamber method, and quantified the abundance of pmoA functional genes using molecular techniques. Moreover, we measured plant biomass and soil physicochemical properties. The results showed that moderate grazing significantly enhanced CH₄ uptake rate and the methane-oxidizing bacteria abundance (i.e., the pmoA gene copy number per gram of dry soil). The pmoA gene copy number ranged from 6.9×10⁴ to 3.9×10⁵ per gram of dry soil in growing season. The CH₄ uptake rate was (68.21±3.01) μg·m^-2·h^-1 under T₁, which was 22.1%, 37.5% and 30.9% higher than that under T₂, T₃ or T₀ , respectively. The CH₄ uptake rate was positively correlated with abundance of CH₄ oxidizing bacteria and soil sand content, but negatively correlated with soil silt content, soil moisture, NH₄⁺-N and NO₃^--N content, and plant biomass. These results suggested that the steppe ecosystem is a CH₄ sink under all land-use types in central Inner Mongolia, and that moderate grazing would enhance methane-oxidizing bacteria abundance and CH₄ uptake by improving soil sand content, reducing soil mineral nitrogen content and plant production in the typical steppe ecosystem. These results were of significance for the development of low-emission grassland management system.

Soil organic carbon dynamics and the prediction of their spatial changes in response to anthropogenically introduced shrub encroachment in desert steppe of the Eastern Ningxia, China.

ZHAO Ya-nan, DU Yan-yan, MA Yan-ping, ZHAO Yan-bing, ZHOU Yu-rong, WANG Hong-mei

2019, 30(6):  1927-1935.  doi:10.13287/j.1001-9332.201906.001

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With the 14-year enclosed grassland and the grazed grassland as control, the impacts of anthropogenic shrublands (Caragana korshinskii) with the different planting years (3, 12, 22 a) and planting spaces (2, 8, 40 m) on soil organic carbon (SOC) contents were examined in the desert steppe of Eastern Ningxia, China. We further analyzed the spatial pattern and heterogeneity of SOC in 0-40 cm soil layer of the grassland area with introduced shrubs. The results showed that SOC in C. korshinskii shrublands had an increase trend with increased planting years and decreased spaces. The mean SOC with different planting years and spaces was 42.7% and 32.8% more than that in grazing land, respectively. There was no significant difference of SOC between shrublands and the 14-year enclosed grassland. The increase trend of SOC decreased by 27.0% in 22-year planting shrubland. The SOC content of 0-40 cm soil layer varied from 0.21 g·kg^-1 to 26.04 g·kg^-1 (with a mean of 3.75 g·kg^-1), and the coefficient of SOC variation ranged from 90.9% to 114.7%. The SOC in 0-5 cm and 15-40 cm soil layers fitted the optimal theory formulation of Gaussian model, while that in 5-15 cm soil layer fitted a spherical model. The ranges (A₀) of spatial autocorrelation in the 0-5 and 5-15 cm soil layers were smaller (3.11, 3.00 km) than that in 15-40 cm soil layer (10.10 km). The nugget/sill C₀/(C₀+C) of SOC in 0-5, 5-15 cm soil layer was 0.2% and 16.3%, indicating a strong spatial correlation, while that in 15-40 cm soil layer was 36.9%, with a moderate correlation. The shrub introdution could significantly accelerate the accumulation and fixation of SOC in top 40 cm soil layer in degraded desert steppe, but also intensified the spatial heterogeneity and SOC fragmentation. The SOC content in the anthropogenic shrublands had no significant difference from that in the enclosed desert steppe (14 years). The SOC spatial heterogeneity and the degree of fragmentation were weakened and decreased with the increasing soil layer depth.

Characteristics of soil greenhouse gas flux and its driving factors in Horqin sand dune-mea-dow wetland cascade ecosystems.

CHENG Gong, LIU Ting-xi, WANG Guan-li, DUAN Li-min, MA Li-qun

2019, 30(6):  1936-1944.  doi:10.13287/j.1001-9332.201906.023

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Using the static chamber-GC technique, greenhouse gas (CO₂, CH₄, N₂O) fluxes of sand dunes and meadow wetlands were measured in a typical sand dune-meadow cascade ecological zone of Horqin. The dynamics of the greenhouse gas fluxes and driving factors were analyzed. The results showed that soil CH₄ flux underwent absorption during the growing season, with average CH₄ fluxes of semi-mobile dunes and meadow wetlands were -52.7 μg·m^-2·h^-1 and -34.7 μg·m^-2·h^-1, respectively, ranging from -176.1 to 49.8 μg·m^-2·h^-1. The peak of CH₄ absorption in the growing season occurred at August 22nd, 2017. In August and September, the months with heavy rainfall, the CH₄ flux in meadow wetlands showed continuous emission, being significantly different from that in semi-mobile dunes. The peak of N₂O flux during the growing season was at July 21st. The monthly average N₂O flux in semi-mobile dunes was following the order of July > August > September > June > May. Soil temperature and moisture were the key factors affecting CO₂ and CH₄ fluxes, whereas the N₂O flux was mainly affected by soil temperature. The soil temperature sensitivity (Q₁₀) showed the sequence of semi-mobile dune (1.009) < meadow wetland (1.474). The water stress rendered the greenhouse gas fluxes in semi-mobile dunes being less sensitive to soil temperature change than that in meadow wetlands.

Spatial pattern and regeneration characteristics of main woody species in natural secondary forest in Maoershan, Northeast China.

SHU Lan, LIU Zhao-gang, DONG Ling-bo

2019, 30(6):  1945-1955.  doi:10.13287/j.1001-9332.201906.026

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Based on the survey data from a 1 hm² plot of the second forest in Maoershan, we divided the stand into four size degrees, including seedlings (tree height H<30 cm), saplings (H 30-130 cm or H>130 cm meanwhile DBH< 5 cm), medium trees (DBH 5-10 cm) and big trees (DBH≥10 cm). The spatial pattern and spatial association of all woody plants and three dominant tree species in four size degrees, as well as the basic forest regeneration, were chosen as study objects, to explore the renewal trend and provide theoretical basis for the sustainable forest management. The O-ring point pattern analysis method was used to analyze the spatial distribution and spatial association. The dominant trees were planted Pinus koraiensis and three common broadleaved tree species (Fraxinus mandshurica, Juglans mandshurica, Phellodendron amurense), and Ulmus pumila. The results showed that the regeneration of the stand was quite common, with 2894 seedlings·hm^-2 and 3337 saplings·hm^-2 . For the whole forest, the seedlings in the stand were positively associated with large trees and medium trees and saplings respectively at the scales of 0-25 m, 0-15 m and 0-40 m, and negatively associated at the subsequent scales. The saplings were positively associated with large trees and medium trees at 0-15 m, 0-25 m respectively, and had no significant association at the subsequent scales. Medium trees showed no significant association with big trees at all the scales. For the dominant trees, the saplings and seedlings of Pinus koraiensis showed negative association at the scale of 0-40 m, while the saplings and seedlings of the three common broadleaved tree species or Ulmus pumila were mainly non-associated. There was a negative association between the saplings of Pinus koraiensis and each size degree of the three common broadleaved tree species or Ulmus pumila at most scale, whereas saplings of the three common broadleaved tree species and Ulmus pumila showed a negative association with non-conspecies only at 0-20 m scale. In the medium and large size degrees, there was no significant association between each two of the three dominant tree species at the scale above 20 m. The secondary forest in Maoershan is still under the process of succession. During the process of forest resource management, measures should be taken to promote the renewal, and the unreasonable spatial pattern should be adjusted in time.

Impacts of thinning on canopy structure and understory light in secondary poplar-birch forests.

SHI Jun-jie, CHEN Zhong-zhen, WANG Guang-hai, JIN Chun-sheng, LI Yong-ning

2019, 30(6):  1956-1964.  doi:10.13287/j.1001-9332.201906.002

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The variation of forest canopy structure and understory light caused by natural or human disturbances might account for environmental heterogeneity and species diversity in the understory. These factors play an important role in driving the structure, process and pattern in forest ecosystem. We set up two 0.25 hm² permanent plots in secondary Betula platyphylla-Populus davidiana forests on the Taoshan Forest Farm, one of which was thinned in 2012 and the other one remained natural. The canopy images of two plots were collected by hemispherical photography technology from 2012 to 2016 and 2018. Analysis of variance and Markov matrix were applied to examine the dynamics of canopy structure, understory light, and canopy closing process after thinning. The results showed that thinning was effective in adjusting canopy structure and understory light availability. Such process lasted for a long time and the adjusting effect decreased over time. After thinning, the change rate of canopy structure and understory light decreased over time. The tree canopy quickly closed during the first three years and then reached a stable state. Understory light availability was positively correlated with canopy openness and negatively correlated with leaf area index. The correlation between understory scattered radiation and canopy structural parameters was the strongest. The correlation between canopy structure and understory light in the thinning plot was stronger than that of the control plot. After thinning, the recovery rate of canopy structure was related to the canopy openness, with larger canopy openness being accompanied with higher recovery rate. Thus, less time was required for the transfer to smaller canopy openness. The Markov matrix model could simulate changes in distributions of canopy structure and could be used to predict the dynamics of the canopy structure.

Seed rain, soil seed bank and seedling regeneration of Quercus aliena var. acureserrata in different slope directions on the middle Qinling Mountains, China

LU Yan-lei, ZHANG Wen-hui, YANG Bin, WANG Ya-nan

2019, 30(6):  1965-1973.  doi:10.13287/j.1001-9332.201906.004

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We studied the seed rain, seed pool quantity and quality dynamics, and seedling develop-ment of natural Quercus aliena var. acureserrata forests in different slopes (sunny, semi-sunny, semi-shady and shady slope) of the middle Qinling Mountains, China. The results showed that seed rain of Q. aliena var. acureserrata generally began at mid-August, peaked from mid-late September to early October, and ended in mid-early November. The dissemination process, occurrence time, and composition of seed rain in four slopes were different. The seed rain intensity of the semi-sunny slope was the highest, which was 134.13 seeds·m^-2, followed by sunny slope, semi-shady slope, and shady slope. The seed rain on the sunny slope occurred first, and the duration of the whole and peak period were the longest. The seed rain on the shady slope occurred at the latest, and the duration of the whole and peak period were the shortest. The seed viability and mature seeds proportion were semi-sunny slope > sunny slope > semi-shady slope > shady slope. From the end of the seed rain to the August of the next year, the size of soil seed bank was semi-sunny slope > sunny slope > semi-shady slope > shady slope. The number of mature, immature and nibbled seeds and seed vigor of soil seed bank showed a decreasing trend with time, while the number of moldy seeds increased. The seeds in soil seed bank mainly existed in the litter layer, followed by the 0-2 cm soil layer, with few seeds in the 2-5 cm soil layer. The seedling density of Q. aliena var. acureserrata was significantly different among the four slopes. The semi-sunny slope, with the highest seedling density, was more suitable for seed germination and seedling growth of Q. aliena var. acureserrata than other slopes.

Assessment of the endangered status and conservation priorities for the rare and endangered plant species in Inner Mongolia, China

LIU Zhe-rong, LIU Guo-hou, GAO Run-hong

2019, 30(6):  1974-1982.  doi:10.13287/j.1001-9332.201906.005

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With 127 rare and endangered plant species of Inner Mongolian in Catalogue of Rare and Endangered Plants in China, China Plant Red Book, National Key Protected Wild Plants List (List No. 1), China Species Red List, Red List of Biodiversity in China: Volume of Higher Plants, List of Rare and Endangered Plants in Inner Mongolia and Atlas of Rare and Endangered Plants in Inner Mongolia as objects, an evaluation system of the threatened grades and conservation priority of rare and endangered plants were built based on data collection and consultation with experts. We set the five criteria, including endangered coefficient, genetic coefficient, utilization coefficient, habitat coefficient, and reproduction coefficient, under which there were 17 subordinate indicators. The analytic hierarchy process was employed to determine the weight of indicators in the system and calculate the endangered grades and conservation priority grades for the rare and endangered species. According to the results of evaluations, two critically endangered (CR) species, 13 endangered (EN) species, 37 vulnerable (VU) species, 44 near threatened (NT) species, and 31 least concern (LC) species were identified, accounting for 1.6%, 10.2%, 29.1%, 34.7% and 24.4% of the total, respectively. Among those species, 52 species were threatened, namely CR, EN and VU species, accounting for 40.9% of the total. The evaluation results of conservation priority grades were: 35 species of Class Ⅰ protected plants, 72 species of Class Ⅱ protected plants, and 20 species of Class Ⅲ protected plants, accounting for 27.6%, 56.7% and 15.8% of the total, respectively. According to the results of evaluation comparison between Red List of Biodiversity in China: Volume of Higher Plants and List of Rare and Endangered Plants in Inner Mongolia, endangered grades of 75 plant species and the protection classes of 62 plant species were calibrated. In this evaluation, the endangered grades of nine plant species and the protection classes of 32 plant species were newly added.

Responses of soil microbial communities in mulberry rhizophere to intercropping and nitrogen application.

XU Zhen-yu, LI Xue-peng, DU Yu, XU Bo-tao, ZHANG Xiu-li

2019, 30(6):  1983-1992.  doi:10.13287/j.1001-9332.201906.037

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In this study, the effects of intercropping with alfalfa and nitrogen application on the functional diversity of soil microbial community in mulberry rhizosphere were examined by Biolog-Ecoplate^TM technique, and principal component and canonical analyses. Compared to monoculture with no nitrogen (N) addition, monoculture with N application and intercropping with alfalfa remarkably reduced soil pH and significantly increased the contents of soil organic matter, soil available N, soil water content, and activities of peroxidase and urease. Monoculture with N application and intercropping with alfalfa (with or without N application) increased the AWCD values, diversity index, and the carbon source utilization ratios of soil microbes. Higher increments of these parameters were detected in the treatment of intercropping plus N application. The results of principal component analysis showed that N application and intercropping changed the capacity of the rhizosphere microbial community for utilizing carbon sources. The utilization of carbon sources highly related to the principal components by the rhizosphere microbial communities was similar in the treatments of monoculture with N application and intercropping without N application. The utilization of itaconic acid and D-glucamaminic acid in the latter was more than 4% and was significantly higher than that in the former. The results from redundancy analysis showed that the soil microbial diversity in mulberry rhizosphere of the treatment of monoculture without N application was positively correlated with polyphenol oxidase activity and negatively correlated with soil water content, whereas that of monoculture with N application and intercropping without N application was significantly positively correlated with soil pH and soil water content and negatively correlated with soil N avalaibility. The diversity of the microbes in the rhizosphere soil of mulberries under the treatment of intercropping with N application showed positive correlation with soil N availability and was significantly negatively correlated with soil pH.

Effects of root growth on dynamics of microbes and enzyme activities during litter decomposition.

HU Kai, TAO Jian-ping, HE Dan-ni, HUANG Ke, WANG Wei

2019, 30(6):  1993-2001.  doi:10.13287/j.1001-9332.201906.022

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To understand the influence of roots of understory plant entering litter layer on litter decomposition in forest ecosystems, we examined the effects of different treatments of Lolium multiflorum root biomass on microorganisms and enzyme activities during leaf litter decomposition of Symplocos setchuensis, a dominant species in a mid-subtropical evergreen broad-leaved forest, through a litter bag simulation experiment. Results showed that diversity index of bacterial and fungal communities of leaf litter surface under three treatments, i.e. no root (N), less roots (L), more roots (M), in a 240-day decomposition process showed the following pattern: M > L > N. The effects of these different root biomass treatments on the composition and quantity of fungal community were more significant than those on bacterial community. The biomass of living roots growing in the litter bag gradually decreased at the end of the growing season of L. multiflorum. The impacts of root growth on the composition of the fungal community gradually decreased during decomposition. At the same decomposition stage, the activities of acid phosphatase, β-glucosidase, polyphenol oxidase, and peroxidase on the litter surface were higher in the treatments with roots than that without roots. These results indicated that root growth could change the composition and quantity of microbial communities and increase the extracellular enzyme activities of microbes, and thus stimulating litter decomposition.

Soil microbial community characteristics in degraded karst tiankeng invaded by Eupatorium adenophorum.

JIANG Cong, SHUI Wei, JIAN Xiao-mei, GUO Ping-ping, CHEN Yi-ping

2019, 30(6):  2002-2010.  doi:10.13287/j.1001-9332.201906.032

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After invading the grand negative landform karst degraded tiankeng, Eupatorium adenophorum will affect the plant diversity, community succession and natural ecological restoration of degraded tiankeng by changing soil microbial community. Taking the degraded tiankeng “Bajiaxiantang” as the research area, the soil around E. adenophorum roots in different habitats was selected to explore the microbial community characteristics of E. adenophorum roots using the Biolog-ECO micro-plate method. The results showed that the invasion degree of E. adenophorum was in order of pit slope shrub-grassland > pit bottom grassland > pit slope forest > pit head shrub-grassland. The characteristics of E. adenophorum varied among different habitats due to habitat heterogeneity. The change of microbial community metabolic activity, dominance index, richness index and evenness index of E. adenophorum roots was closely related with the invasion degree, with significant diffe-rence between inside and outside of the tiankeng. Amino acids and polymers were the main carbon sources utilized by soil microorganism. The α diversity of herbaceous plants in different habitats were correlated with that of soil microbial community. The diversity of soil microbial community around E. adenophorum roots increased significantly with the increases of invasion level, which could form a microenvironment conducive to invasion and colonization. In the future, the degraded tiankeng would eventually form the climax community of underground forests with community succession and natural ecological restoration, which might result in the disappearance of E. adenophorum in the degraded tiankeng.

Light response process and simulation of Dendrocalamopsis oldhami in the process of gradual water loss.

DU Lan, XIA Jie, LI Hai-hua, WU Wei, CHEN Liang, ZHANG Wei, CHEN Sheng, XIE Jin-zhong

2019, 30(6):  2011-2020.  doi:10.13287/j.1001-9332.201906.006

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The photosynthesis response of the leaves of 2-year-old potted Dendrocalamopsis oldhami seedlings under continuous and multistage soil moisture was measured and analyzed by using a porta-ble photosynthetic system (Li-6400) during the natural water consumption process from artificial watering to saturated soil water. The results showed that there was less obvious photoinhibition in leaves of D. oldhami grown in the region where the relative soil water content (SRWC) was from 53.5% to 95.6%. There was a higher net photosynthetic rate in relative water deficit environment with the relative soil water content from 53.5% to 69.6%. When SRWC was below 33.6%, there was a significant photoinhibition. When the relative soil water changed, the P_{n max} value simulated by rectangular hyperbola model was much higher than measured value. The simulated light saturation point (LSP) value fitted by the rectangular hyperbola model, the non-rectangular hyperbola model and the exponential model was much lower than the measured value, and the simulation of the light-response curve under extreme water shortage conditions had larger differences between the fitted values and the observed data. Both the stomatal limitation value (L_s) and water use efficiency (WUE_inst) showed a similar response process as the relative soil water decreased. Both of them increased first and then decreased, with the maximum value appeared in the range of 53.5%≤SRWC≤69.6%. Such a result showed a similarity and representative with the P_{n max} of photosynthesis light-response processes under changing soil moisture. The optimal humidity management range of SRWC for normal photosynthesis in leaves of D. oldhami was from 53.5% to 69.6%. In addition, it had good adaptability to higher soil water content (69.6%≤SRWC≤95.6%). Rectangular hyperbola modified model could well simulate the light-response of photosynthesis under different soil water conditions (23.1%≤SRWC≤95.6%), while the other three models had their own limitations.

Fraction of absorbed photosynthetically active radiation over summer maize canopy estimated by hyperspectral remote sensing under different drought conditions.

LIU Er-hua, ZHOU Guang-sheng, ZHOU Li

2019, 30(6):  2021-2029.  doi:10.13287/j.1001-9332.201906.041

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Fraction of absorbed photosynthetically active radiation (fAPAR) is one of the important remote sensing model parameters of vegetation productivity. However, the crop canopy fAPAR estimation during growing season under different drought conditions has not been reported yet. In this study, the characteristics of summer maize canopy fAPAR and spectral reflectance during growing season under different drought stresses and the relationships of fAPAR with reflectance, the first derivative spectral reflectance and vegetation indices were examined based on the hyperspectral reflectance and fAPAR data from the summer maize drought manipulation experiment with five irrigation levels in 2015. Under mild water stress and sufficient water supply conditions, fAPAR was higher, with the maximum value of 0.7. Under severe water stress and severe persistent drought, fAPAR was lower, with the minimum value of 0.06. Reflectance of visible and shortwave bands increased and near infrared reflectance decreased with increasing drought. The fAPAR was negatively related with visible bands and shortwave bands, but positively correlated with near infrared. Visible and shortwave band reflectance had significant correlation with fAPAR, especially at 383, 680 and 1980 nm, with all the correlation coefficients being more than -0.87. The strong and stable relationship between the first derivative spectral reflectance and fAPAR appeared at 580, 720 and 1546 nm, with the correlation coefficients being -0.91, 0.89 and 0.88, respectively. There were linear or logarithm relationships between fAPAR with nine vegetation indices. Among the nine indices, the enhanced vegetation index (EVI), renormalized difference vegetation index (RDVI), soil adjusted vegetation index (SAVI), and modified soil adjusted vegetation index (MSAVI) performed well with the correlation coefficient being higher than 0.88, and the average relative error (RMAE) 16.6%, 16.6%, 16.7% and 16.2%, respectively. Based on the logarithmic relationship between first derivative spectral reflectance and fAPAR, the simulation effect was best at the band of (720±5) nm, with a correlation coefficient of 0.86. The correlation coefficient of the relationship between fAPAR and reflectance was less than 0.81. The results could provide fAPAR simulation for remote sensing model of vegetation productivity and drought warning.

Effect of Miscanthus planting on the structure and function of soil bacterial community.

DUAN Peng-fei, CHEN Yan, ZHANG Fei, HAN Hui, PANG Fa-hu, CHEN Zhao-jin, TIAN Wei

2019, 30(6):  2030-2038.  doi:10.13287/j.1001-9332.201906.038

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Miscanthus is a promising candidate species of second-generation energy crops. To our knowledge, the composition and function of Miscanthus rhizosphere bacterial communities has not yet been reported. In this study, rhizosphere soil samples were collected from Miscanthus (Xiangzamang No. 1) which was grown in Nanyang City for five years and bareground (as the control) to analyze the bacterial community structure and diversity using 16S rRNA gene sequencing on the Illumina MiSeq platform. PICRUSt was used to determine the metabolic and functional abilities of soil bacterial communities. Phylogenetic analysis based on 16S rRNA gene sequences showed that sol bacteria could be divided into 23 phyla and 231 genera, with high richness of the community composition. The dominant phyla were Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, Bacteroidetes and Gemmatimonadetes. The bacterial community diversity in the rhizosphere samples of Xiangzamang No. 1 was lower than that in unplanted samples. Rhizosphere bacterial communities were affected by Miscanthus crops. Based on the PICRUSt analysis of bacterial community functions, our results revealed a wide genetic diversity of organisms involved in various essential processes,such as amino acid transport and metabolism, cell wall/membrane/envelope biogenesis, signal transduction mechanisms. Based on the 16S rRNA gene copy number of the detected phylotypes, 22 bacterial metabolic function in the rhizosphere samples of Miscanthus was higher than that in bareground. Results from N- and P-cycling gene analysis showed that Miscanthus planting altered the N- and P-cycling metabolic capacities of soil bacteria.

Community structure and distribution pattern of small mammals in agricultural area of Yunnan Province, China.

CHEN Xing, LIU Zheng-xiang, DU Chun-hong, HONG Mei, GONG Zheng-da, SHAO Zong-ti, DUAN Xing-de, GAO Zi-hou

2019, 30(6):  2039-2048.  doi:10.13287/j.1001-9332.201906.036

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To understand the characteristics of community structure and spatial distribution of small mammals in agricultural area of Yunnan Province, a systematic investigation was carried out in 104 quadrats of 25 regions in Yunnan Province from August 2010 to April 2018 by rat trap night method. The spatial variation of community characteristics along environmental gradients was analyzed by community ecological indicators. The results showed that a total of 3240 small mammals were captured and cold be classified into 42 species in 21 genera, 9 families, and 4 orders. The largest number of small mammal was rodents, dominated by Apodemus chevrieri and Rattus tanezumi. The 25 regions were clustered into three classes. The altitudinal distribution of small mammals was similar to the latitudinal distribution in agricultural areas. The number of species was relatively less in the low latitude and altitude range, with Rattus spp. and Mus spp. as the dominant species. In the high latitude and altitude region, the dominant species changed into Apodemus, Niviventer and Eothenomys. With the increases of altitude, the diversity index showed unimodal distribution, with the highe-st species diversity occurred in the mid-altitude area. The diversity index of small mammal showed the “V” type pattern in longitude, being the highest in the 98°-99° E gra-dient zone. At the latitude level, it showed an overall upward trend from south to north. Results from the GAM analysis showed that the degree of influence on the small animals in the agricultural area was in order of longitude, altitude and latitude. The similarity analysis in the composition of small mammals showed that the moderate similarity occurred in the adjacent gradient zone, and the highest similarity occurred in middle altitude zone, middle latitude zone, and low longitude zone. The farther the distance between different gradient zones, the lower the similarity of community structure. There was high spatial heterogeneity in different dimensions of small mammals’ community structure in Yunnan Province. The geographical distribution trend of species diversity showed different distribution patterns across environmental gradients.

Effects of enrofloxacin and Cu combined pollution on the activities of digestive enzymes of earthworm in soil.

ZHANG Wei, ZHANG Meng, CHEN Kai, JIN Yu-he, YAN Hui-yi, HU Yan-mei, JIN Lan-shu

2019, 30(6):  2049-2055.  doi:10.13287/j.1001-9332.201906.034

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The effects of single and combined pollution of enrofloxacin and Cu on the digestive enzymes of earthworms were studied, based on the actual pollution of caused by the application of livestock feces in farmland soil. Results showed that single enrofloxacin (0.1-4 mg·kg^-1, 28 d) did not affect protease, but inhibited cellulase and alkaline phosphatase, with an induced effect on acid phosphatase. Single Cu pollution (20-200 mg·kg^-1, 28 d) had inhibitory effects on the four digestive enzymes in earthworms. The effects of combined exposures on the digestive enzymes were mainly negative, showing a synergistic increasing character of toxicity in cellulase and acid phosphatase activities. The response dynamics of digestive enzymes to exposure duration was regulatory response (3 d)-intense response (7 d)-reaction recovery (14 d)-chronic exposure (28 d). Chronic exposure results showed that the combined treatments containing high-dose pollutant (200 mg·kg^-1 Cu or 4 mg·kg^-1 ENR) had more ecological risk.

Screening of pyrene degradation bacteria strain from the Kochia scoparia roots and its potential for promoting growth

CAO Yang, SONG Li-chao, NIU Xu-guang, ZHANG Wei, LIU Xin-zheng, WU Shan, LI Si-nan, LI Hai-yan

2019, 30(6):  2056-2062.  doi:10.13287/j.1001-9332.201906.031

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The endophytic bacteria were isolated from the roots of polycyclic aromatic hydrocarbon (PAHs)-tolerant plant. We investigated their ability of PAHs degradation and plant growth promo-ting, with the aim to provide theoretical support for bacterial-plant cooperative soil remediation. Kochia scoparia living in coking plant area were selected for strains isolation. Eight endophytic bacteria strains, which used pyrene and 1-aminocyclopropane-1-carboxylic acid (ACC) as sole carbon and nitrogen source, were isolated from the roots of K. scoparia. Three endophytic bacteria, KSE4, KSE7 and KSE8, displayed high degradation efficiency in pyrene degradation experiment. They were identified as Bacillus sp., Pseudomonas sp., and Sphingobacterium sp., respectively. The abili-ties of those three strains to produce ACC deaminase and their effects on seed germination of K. scoparia were examined under pyrene stress through liquid culture tests. The results showed that the activity of ACC deaminase decreased with increasing pyrene concentration (0-15 mg·L^-1). KSE7 had the strongest promotion effect. When pyrene concentration reached to 15 mg·L^-1, the germination rate and bud length of K. scoparia increased by 44.8% and 61.1%, respectively. Our results indicated that KSE7 is a promising bacterial strain for soil remediation in coking plant area.

Arbuscular mycorrhizal fungi enhance cadmium uptake of wetland plants in contaminated water

NING Chu-han, LI Wen-bin, XU Qi-kai, LI Min, GUO Shao-xia

2019, 30(6):  2063-2071.  doi:10.13287/j.1001-9332.201906.019

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Arbuscular mycorrhizal fungi (AMF) play an important role in plant growth enhancement, tolerance to heavy metal toxicity, and rehabilitation of contaminated ecosystems. An experiment was carried out with Phragmites communis and Pennisetum alopecuroides inoculated with or without Funneliformis mosseae (Fm), or Rhizophagus intraradices (Ri) under the simulated wetland system with Cd polluted water (0, 5, 10 or 20 mg·L^-1). The results showed that Cd addition significantly decreased mycorrhizal colonization. AMF increased plant height, dry mass, leaf chlorophyll, N and Cd contents in shoot and root of P. communis and P. alopecuroides, enhanced Cd enrichment capability by roots, and decreased Cd transfer coefficient. Under Cd 5 mg·L^-1 treatment, all of the indices in Fm + P. communis combination treatment were higher than those of other treatments, with 60.6% of AMF colonization, and the entry points and vesicles per mm root length were 2.3 and 3.7, respectively. Under the inoculation treatment, dry mass of shoot and root was improved by 69.1%, and 75.0%, nitrogen contents in shoot and root were increased by 38.7% and 27.8%, and the chlorophyll content and plant height were increased by 3.8% and 11.1%, respectively. There was a significant positive correlation between Cd concentration in wetland system and Cd content in shoot and root. Under Cd 20 mg·L^-1 treatment, Fm + P. communis combination had the maximum Cd contents of 182.4 mg·kg^-1 and 663.3 mg·kg^-1 in shoot and root, respectively, the lowest Cd transfer coefficient (0.27), and the highest enrichment coefficient (0.55). In conclusion, Fm + P. communis was the best combination for absorbing Cd in polluted water.

Effects of light intensity on growth, survival, metabolism and related enzyme activities of Sepia pharaonis.

ZHOU Shuang-nan, CHEN Qi-cheng, JIANG Mao-wang, JIANG Xia-min, PENG Rui-bing, HAN Qing-xi, HUANG Chen, ZHAO Chen-xi, LI Jian-ping

2019, 30(6):  2072-2078.  doi:10.13287/j.1001-9332.201906.033

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An experiment with single-factor design was conducted to investigate the effects of light intensity on growth and survival of cuttlefish (Sepia pharaonis). The specific growth rate, survival rate, oxygen consumption rate, ammonia excretion rate, lactic acid content in muscle, respiratory metabolic enzymes (including hexokinase, pyruvate kinase, and lactate dehydrogenase), supero-xide dismutase, and malondialdehyde in liver were measured in five constant light intensity treatments (10, 30, 50, 70, 90 μmol·m^-2·s^-1). The main results were as follows: The specific growth rate and survival rate remained steady initially and then decreased gradually with the increases of light intensity. There was no significant difference between groups 10 and 30 μmol·m^-2·s^-1, but they were significantly higher than those of the other groups. Exposed to light intensities of 10 and 30 μmol·m^-2·s^-1, the specific growth rates were (8.43±0.22)%·d^-1 and (8.47±0.17)%·d^-1, and the survival rates were (79.2±5.9)% and (80.0±4.9)%, respectively. Oxygen consumption rates and ammonia excretion rates increased first slowly and then sharply, and reached the maximum value when light intensity was 90 μmol·m^-2·s^-1, which was significantly higher than those of the other groups. Lactic acid content in muscle firstly decreased and then increased, with the minimum value at 30 μmol·m^-2·s^-1. The acid content of 10 μmol·m^-2·s^-1 was significantly lower than those of the other groups except 30 and 50 μmol·m^-2·s^-1. With the increases of light intensity, the activities of HK and PK in gills remained steady initially and then decreased gradually, and reached the highest level when exposed to 10 and 30 μmol·m^-2·s^-1, which were significantly higher than those of the other groups. LDH activity in muscle had the lowest level at the light intensity of 10 and 30 μmol·m^-2·s^-1, which was significantly lower than those of the other groups. SOD activity in liver firstly increased and then decreased, and reached the highest level ((104.93±4.17) U·mg^-1 pro) when exposed to 70 μmol·m^-2·s^-1, which was significantly higher than those of the other groups. MDA content in liver first remained steady and then increased gradually, and reached the highest level ((5.06±0.35) nmol·mg^-1 pro) when exposed to 90 μmol·m^-2·s^-1, which was significantly higher than those of the other groups. In conclusion, the optimum light intensities for growth, survival and metabolism of S. pharaonis were 10 and 30 μmol·m^-2·s^-1, beyond which S. pharaonis would be under stress. Therefore, sunproof measures should be taken to keep weak light condition in culture practice.

Seasonal variation of phytoplankton community and its relationship with environment in subtropical reservoirs: A comparison between two methods of functional groups classification

ZHU Yi-qiu, LYU Jun, LI Qiao-zhen, ZHANG Xiao-li, HU Ren, XIAO Li-juan

2019, 30(6):  2079-2086.  doi:10.13287/j.1001-9332.201906.030

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Phytoplankton is the most important biological component in the reservoir ecosystem, which could indicate the status of aquatic ecosystem due to its sensitive to environmental variation. To understand the application and difference between two methods of phytoplankton functional group classification, functional groups (FG) and morphology-based functional groups (MBFG), in indicating the changes of reservoir environment, we investigated water quality and phytoplankton in Qingshitan Reservoir monthly from March 2016 to February 2017. Two phytoplankton functional groups classifications (FG and MBFG) were used to analyze phytoplankton community composition, seasonal succession, and its driving factors. We compared the application and differences of two methods of functional group classifications in indicating environmental changes. The results showed that there were 109 species belonged to seven phylum, which could be classified into 17 FG or 5 MBFG functional groups. Results from both methods indicated that the reservoir was meso-eutrophic. The phytoplankton seasonal succession under 8 or 9 steps with FG or 8 steps with MBFG. Results from the redundancy analysis showed that the response of phytoplankton community reflected with FG to environmental variation was more sensitive than that with MBFG, especially in the response to the changes of pH and nitrate concentration. In conclusion, FG was more appropriate in describing community succession and exploring the relationship between phytoplankton and environment.

Effects of salinity on the survival and asexual reproduction of Aurelia coerulea polyps at different temperatures

XING Yong-ze, ZHANG Mei, ZHEN Yu, MI Tie-zhu

2019, 30(6):  2087-2092.  doi:10.13287/j.1001-9332.201906.021

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The scyphozoan genus Aurelia is one of the main contributors causing jellyfish blooms in global coastal waters. The population and reproduction of polyps are important factors to the outbreak of jellyfish. In this study, the effects of different salinity on the survival and asexual reproduction of Aurelia coerulea polyps were explored, which were cultured at the high (21 ℃) and low temperature (12 ℃), respectively. The results showed that more than 90% polyps could survive in the salinity range of 15-40 at the high temperature, with a range of salinity for budding being 20-32 and an optimum value of 28. The polyps were able to produce podocysts to tolerate low (≤15) and high (≥36) salinity conditions. At the low temperature, the survival rates of polyps were more than 90% in the salinity range of 20-40. The polyps could produce more buds in the salinity range of 20-32, with an optimum of 28. The salinity range of 20-40 was suitable for strobilation, with an optimum range of 28-32. It is concluded that the polyps of Aurelia coerulea can tolerate wide salinity variations, and that the salinity in a certain range has no significant influence on the asexual reproduction of polyps.

Effectiveness of otolith strontium marking for juvenile Cyprinus carpio.

QIU Chen, JIANG Tao, CHEN Xiu-bao, LIU Hong-bo, YANG Jian

2019, 30(6):  2093-2100.  doi:10.13287/j.1001-9332.201906.027

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In this study, we evaluated the effectiveness of SrCl₂·6H₂O to mark otoliths of juvenile common carp (Cyprinus carpio). The carp fish were immersed with four concentrations of the Sr compound (i.e., 0, 4, 8, 12 mg·L^-1) for 2 d to determine the essential concentration for immersing. Then, the carp fish were immersed in 8 mg·L^-1 of the Sr compound for five different immersing times (i.e., 1, 2, 3, 4, 5 d) to establish the essential immersing time. Results from electron microprobe analysis (EPMA) showed that otolith Sr marks were very obvious in all C. carpio fish of the aforementioned Sr immersed group with high ratio of Sr/Ca concentration and red color (high Sr level) ring map, compared to the control group with low ratio of Sr/Ca concentration and basic blue color (low Sr level) map. We obtained a 100% mark-success rate of otolith Sr marking in juvenile C. carpio. No significant difference were observed on the average body length, mass and mortality between the immersed group and the control group, suggesting that Sr marking had no negative impact on fish. As clear and complete otolith Sr marked rings occurred at concentration of 8 mg·L^-1 or more, and immersing time of 2 d or more for the Sr compound, 8 mg·L^-1 and 2 d were suggested as the essential immersing Sr concentration and immersing time, respectively. Our results demonstrated the strong feasibility of otolith Sr marking for juvenile C. carpio.

Effects of tourism disturbance on the habitat and water quality for Andrias davidianus in Zhangjiajie, Hunan, China

LUO Qing-hua, TONG Fang, TAO Shui-xiu, CAO Wei, FU Lei, ZHU Shen-hai

2019, 30(6):  2101-2108.  doi:10.13287/j.1001-9332.201906.039

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To understand the effects of tourism disturbance on the habitat and water quality for Chinese giant salamander (Andrias davidianus, CGS), the interference and characteristics of habitat for CGS under different tourism intensity (high, medium, and low) were investigated, and the physicochemical and microbial index of water were analyzed in Zhangjiajie City, Hunan Province, China from 2014 to 2016. The results showed that high tourism disturbance (>0.5 million per year) significantly increased noise and reduced the number of dens, decreased dissolved oxygen levels, increased total nitrogen, total phosphorus, and microbial abundance in water, especially that of Escherichiacoli. Under high disturbance, the characteristics of habitat and water quality still could meet the requirements of the growth of CGS. According to the National ground water class Ⅱ standard based on the demands of E. coli in the surface water (2000 ind·L^-1), the theoretical threshold of tourist numbers was 26.0471 million per year. The intensity of tourism interference should be effectively reduced by declining tourist numbers and tourism facilities, for the protection of the habitat quality of the CGS and the promotion of tourism development.

Phototaxis of Anguilla marmorata based on fish attracting technology of eel passage

MO Wei-jun, HE Zhen-jun, YANG Yu, LIU Chao, WANG Bin, WANG Jian-ping

2019, 30(6):  2109-2115.  doi:10.13287/j.1001-9332.201906.025

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Light trap is commonly used in protecting Anguilla marmorata resource and improving the attraction of eel passage entrance. In this study, a self-made multifunctional round pool was used to explore the phototaxis of elvers (A. marmorata) under three conditions. 3 W underwater landscape lamp was used as the light source. The results showed that the percentages of juvenile A. marmorata occurrence in light zone and dark zone were (8.7±0.3)% and (3.6±1.7)%, (8.4±0.2)% and (5.0±1.4)%, (9.0±0.2)% and (1.9±1.3)% respectively under three conditions. Moreover, most glass eel distributed in the light zone, while elver (or elver develop) distributed in the dark zone. The primary regions of fish occurrence and its percentages were yellow zone [(29.4±4.9)%], red zone [(24.1±3.9)%)] and purple zone [(17.2±4.0)%] for condition one, yellow zone [(29.4±3.3)%], purple zone [(25.2±3.7)%] and red zone [(18.2±2.9)%] for condition two, and red zone [(33.3±2.3)%], purple zone [(25.6±3.8)%] and yellow zone [(20.7±5.7)%] for condition three. Correspondingly, the top three regions of fish first entering were red, yellow and purple, red, purple and yellow, and red, purple and yellow, respectively. The number of entering and exiting for fish in those three color zones was between blue-green zone and colorful zone. Visual fatigue would occur for elvers with continuous exposure to red light or yellow light. Our results suggested that the phototaxis of elvers is dependent on their developmental stages. Glass eels have phototaxis and seem to be more interesting in red, yellow, and purple light. Light guidance fish is available in the entrance of eel passage, which can help glass eels find the migration channels.

Reviews

Optimizing MaxEnt model in the prediction of species distribution.

KONG Wei-yao, LI Xin-hai, ZOU Hong-fei

2019, 30(6):  2116-2128.  doi:10.13287/j.1001-9332.201906.029

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Maximum Entropy (MaxEnt) model has been widely used in recent years. However, MaxEnt is highly inclined to produce misleading results if it is not well optimized. We summarized the researches about the model optimization for sampling bias correction, model complexity tuning, presence-absence threshold selection, and model evaluation. Spatial filtering performs best for sampling bias correction, while restricted background method shows the lowest efficacy. Model complexi-ty is mainly determined by three factors: The number of environmental variables, model feature types, and regularization multiplier. Variables filtering is needed when sample size is less than the number of environment variables. The criterion of variables selection should focus on their ecological significance rather than the co-linearity between them. The choice of feature types has relatively limi-ted effects on predictive performance of the model, therefore it is advised to choose simpler models. To control overfitting, it is necessary to conduct species-specific tuning on regularization multiplier, which was usually bigger than the default setting. There are three criteria called objectivity, equality and discriminability for selecting threshold to convert continuous predication (e.g. probability of presence) into binary results. Maximizing the sum of sensitivity and specificity is a sound method for threshold selection. Model evaluation methods could be classified into two main types: Threshold-independent and threshold-dependent. Among the threshold-independent evaluations, information criteria may offer significant advantages over AUC and COR. True Skill Statistics is a better index for threshold-dependent evaluations, because it takes both omission and commission errors into account, and is robust to pseudo-absence assumption and species prevalence.

Research advances on resource and biological control of endoparasitic fungi.

LIU Zi-qing, WAN Yi-le, HAO Yu-e

2019, 30(6):  2129-2136.  doi:10.13287/j.1001-9332.201906.020

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Endoparasitic fungi are a group of nematophagous fungi which produce a variety of special spores to infect free nematodes. They play a key role in maintaining the population density of nematodes in the natural systems. Moreover, they are important materials for the study of species diversity. Therefore, they have special research significance and economic values. At present, many studies mainly focus on the infectivity of trapping fungi to nematodes, and mainly directed at the second instars larvae. However, the endoparasitic fungi have infectivity to nematodes at all stages. Here, we reviewed the resource status, diversity of spore morphology, infection modes, life history and host of endoparasitic fungi, and the biocontrol fungi with development potential and their commercialized application. Finally, we proposed some suggestions for future researches.